The experiments proposed here will examine properties of the dynamic stability of the movements produced by the nervous system. These experiments will focus on the movements produced by neural systems located within the spinal cord, characterizing first how the movements respond to dynamic perturbations and second how these neural systems are organized for the production of stable movements. The basic results from these experiments will therefore provide important information about the role of the spinal cord in the production of movement. By describing the limits and extent of the control of stability by spinal motor systems, we will gain a better understanding of how this control can be augmented and exploited to produce purposeful movements when the spinal cord is isolated. These experiments are designed primarily to provide such information. At the same time, these experiments are designed to examine an exciting and potentially powerful hypothesis of the production of movement by the nervous system. If these experiments find that spinal motor systems produce stable movements through the implementation of a version of sliding control, this motor systems produce stable movements through the implementation of a version of sliding control, this will be of fundamental importance in our understanding of the neural control of movement. However, we stress that the results from these experiments have been designed to provide important information on their own, regardless of whether or not they are consistent with this novel hypothesis.